If you had a previous installation of Aptana Studio in hardy and now that you've upgraded to ibex it no longer works then you aren't alone. It no longer works since during the upgrade Firefox 2 was removed from your system, and there isn't a way to put it back in as its been removed from the package manager.
After finally giving in I decided to work out how to get Firefox 2.0.0.11 and 3.0.1 running side by side. It turned out to be much easier than I thought, so I thought I'd share this with the world (although its probably posted on about 5million other blogs), either way...
If you've ever worked with Firebug you'll know its possibly the best tool out there for aiding in web development within Firefox; thankfully there are some really handy extensions for it to make it even more indispensable!